Human antigen R (HuR) regulates Cigarette Smoke-induced inflammation: Implications in COPD

Abstract

Chronic Obstructive Pulmonary Disease (COPD) is an incurable and prevalent respiratory disorder that is characterized by chronic inflammation. This inflammation is typified by an increase in inflammatory cells and mediators such as interleukin-8 (IL-8) and cyclooxygenase-2 (COX-2). COPD is primarily caused by cigarette smoke (CS) and other noxious particles (e.g. air pollution). Cigarette smoke may contribute to lung inflammation via human antigen R (HuR), a ubiquitously-expressed RNA-binding protein that regulates the stability of mRNA encoding proteins that are associated with inflammation; this would indirectly increase expression by facilitating translation of the mRNA. In order for HuR to stabilize target mRNA, HuR translocate from the nucleus to the cytoplasm. However, the expression and localization of HuR in COPD or its molecular regulation by cigarette smoke is not known. Therefore, we hypothesize that cytoplasmic translocation of HuR contributes to inflammatory protein production in response to cigarette smoke, including those that are increased in COPD. The aims of this study are (1) to evaluate the expression and localization of HuR in human lung tissue and structural cells from Normal (never-smokers without COPD), Smokers (without COPD) and COPD subjects and (2) to assess if HuR regulates cigarette smoke-induced inflammatory protein production. First, by using multiplex Immunohistochemistry (mIHC), we found that there was more cytoplasmic localization of HuR in lung tissue from Smokers and COPD subjects compared to Normal subjects, where HuR was predominantly localized in the nucleus. There was also more cytoplasmic HuR in macrophages from Smoker and COPD lung tissue. In vitro, in primary human lung fibroblasts (HLF), there was a slight increase in total HuR protein in Normal and COPD HLF after exposure to 2% cigarette smoke extract (CSE), an in vitro surrogate for cigarette smoke exposure. After 4 hours of CSE exposure, there was an increase in cytoplasmic HuR. Surprisingly, the protein and mRNA levels of COX-2 and IL-8 were significantly higher in siHuR-transfected cells exposed to 2% CSE for 24 hours compared to siCtrl-transfected cells. Finally, Knock-down of HuR did not affect the decay of cox-2 and Il-8 mRNA in response to 2% CSE. This study is the first that investigate the role of HuR in regulating cigarette smoke-induced inflammation which could provide the basis for the development of new target therapy for diseases such as COPD.